Electric graphitizing furnace



Patented Dec. 9, 1952 UNITED STATES PATENT OFFICEl ELIEKJ'IR'ICV GRAPHITIZING FURNACE Paul R. Jnckniess, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of'Delaware Application June 6, 1951, Serial No. 230,170v

3` Claims. 1

They invention relates to furnaces particularly those suitable for graphitizing carbon articles. It more particularly concerns an improved electrically heated graphitizing furnace in which carbon plate-s are passed through the furnace in succession to produce a continuous succession of graphite plates.

One of the objects of the invention is to provide an electrically heated graphitizing furnace in which objects to be graphitized become heated, graphitized, and cooled in one continuous passage through the furnace.

Another object is to provide an electrically heated graphitizing furnace in which the heat Contained in the objects freshly graphitized therein is largely recovered in heating additional objects to be graphitized.

Another object is to provide a graphitizing :furnace in which the heating, graphitizing, and cooling of the article is accomplished inv a relatively short time with. a relatively low consumption of electrical heating energy.

A particular object of the invention is to provide an electrically heated graphitizing furnace which is capable of heating, graphitizing, and cooling a continuous succession. of carbon slabs.

With the above and other objects in view, the inventionv has particular relation to certain novel features of construction, arrangement of parts and use, an example of which is given in this speciiication and illustrated in the accompanying drawingwherein:

Fig. l is a longitudinal elevation, withl parts cut away to reveal structure, showing a complete embodiment of the invention.

Fig. 21 is a transverse sectional elevation oi the apparatus on the line 2--2 of Fig. 1.

Fig. 3 is a transverse sectional elevation on the line 3--3 and cn the line 3*--3' of Fig. l.

Referring to the drawing in general, the apparatus shown comprises a heat generating compartment l, a tunnel 2 comprising a graphitizing zone 3 below the heat generating compartment I, and heat exchange zones 4. and 5 extending from either end respectively of the grap-hitizing zone. The heat generating compartment and tiuinel` are covered by thermal insulation e. .g.

lamp black, conta-ined in the housing 'i which encloses the top, bottom, and sides of the tunnel and heat generating compartment.

These several portions of the apparatus be built up of suitable refractory materials including graphite slabs and bricks, graphite being mandatory at least in the graphitizingv zone Where extremely high temperatures prevail. In

this modek of construction, the bottom 8 of the housing I comprises slabs 9 laid transversely of the tunnel with their ends resting upon foundation Walls I9 and Il respectively which extend from one end of they tunnel tothe other. Similar foundation walls I2 and I3 may be provided intermediate the ends of the transverse slabs S. As shown, the bottom 8 has a mid-section I4 and two end sections I5 and I6, the midsection being recessed below the end sections.

Extending lengthwise through the tunnel 2 is a pair of rails l'I and IS resting on end sections I5 and I6. `Additional supports I9 for the rails are provided over the door of the mid-section I4. The tunnel 2 has side walls 20 and 2| which are sup-ported on the bottom 8. The heat generating compartment has open sides 22 and 23 but closed. end walls 24 and 25, respectively, the ends of which rest on side walls 20 and 2|, respectively. The top of the heat exchange zones 4 and 5 of the tunnel are closed by cover slabs 2B, the ends oi which rest on side walls 20 and 2|. The top of the heat generating compartment is. closed by slabs 2l, the ends of which restr on end walls 24 and 25, respectively. The bottom of the heat generating compartment is closed by the slabs 28, the opposite ends of which are supported in grooves 29 and 30 near the inside bottom edge of' the ends 24 and 25', respectively; End walls 3-I and 32, respectively, are provided at each end of the housing 'I transversely of the ends of the tunnel. Each end wall is provided with a horizontally disposed slot' 33 and 34 as an` opening or entrance to each end of the tunnel 2. The sides of the housing are closed by side walls 69 and 19.

Longitudinally disposed slots 35 and 36 are provided in the sides SilA and lil, respectively, of'

the housing 'I through which extend theA oppcsite ends of the electrical.v resistance heating elements 3l, 38, 39, and 49, which pass through the opening sides ofA the heat generating compartment. Terminals 4I and 42 are clamped on opposite ends of the resistance heating elements forpassing the electrical heating current through ther elements from cables 43 and 44. The terminals are provided with cooling water entrance and exit pipes 45 and 4S, respectively.

Opposite each end of the tunnel 2 is a reciprocating' motor 4f! and 4S, the piston rods I9Y and 5'of which, respectively, are arranged to reciprocate toward and away from the tunnel entrances (slots) 33 and 34, respectively.

A ramp 5I leads up to the tunnel entrance 33. the upper surface 52 being positioned to receive graphitized articles as they come off the rails and out of the tunnel opening 33. A platform 53 is arranged outside the tunnel entrance 33 above the ramp l so that the bottom surface 54 is above graphitized articles coming out of the tunnel opening 33. At the opposite end of the tunnel is placed the upwardly sloping ramp 55 having a pointed leading bottom edge 5B in position to guide articles leaving the tunnel entrance 33 onto the top surface 51 of the ramp 55. A platform 58 is provided below the ramp 55, having its upper surface 53 level with the top 58 of the rails.

In addition to the insulating ll 6, similar insulation is placed in the space 6I between cover slabs 27 and the top heating elements 31, 38, 39 and 40, and inside the tunnel filling the spaces 62 therein below the top 60 of the rails. Vent tubes 63 and 64 may be provided for each heat ex.. change section of the tunnel, respectively.

In starting the furnace, a bottom layer of articles to be graphitized, e. g. slabs 65, is formed on rails I! and I8 as by laying a succession of slabs on platform 53 and then shoving each slab sidewise, one behind the other, into the tunnel 2 through slot 34 onto rails Il and I8, the shoving being accomplished by means of piston rod 50 actuated by reciprocating motor G8. Slabs are thus shoved into the furnace through slot 34 until slabs emerge from the other end of the tunnel through slot 33 and slide down ramp 5| as indicated. At this stage, a top layer slab 6B is formed over the rst by laying a succession of slabs on platform 53 and shoving each slab sidewise, one behind the other, through slot 33 into the tunnel over the bottom layer of slabs therein with the aid of piston rod 49 actuated by reciprocating motor 47 until slabs emerge from slot 34 and slide up onto the ramp 55. The emergent slabs may be removed from ramps 5| and 55 in any convenient manner.

Meanwhile, a suitable E. M. F. is applied to the terminals 4| and 32 so as to produce a current flow in the heating elements 3l', 38, 39, and 40 to heat them. The heating elements, thus heated, radiate heat to the cover members 28 which in turn radiate heat to the slabs 65 in the top layer. As the slabs in the top layer become heated, they conduct heat to the slabs 65 in the underlying layer. The temperature of the heating elements is made suiiiciently high to raise the temperature of the slabs lying below the heat generating compartment to graphitizing temperature. When the heat generating compartment is thus heated to working temperature, additional slabs to be graphitized are introduced sidewise as before into the tunnel from opposite ends so that both layers move in opposite directions While the top layer slides over the top of the bottom layer. Inasmuch as the top layer of slabs is in contact with the bottom layer during the time the slabs travel through the furnace, the hottest slabs, i. e. those in both layers moving away from under the heat generating compartment where graphitization is completed, exchange some of their heat to those moving toward the heat generating compartment. Thus, there is an exchange of heat from the freshly graphitized slabs to the cooler incoming ungraphitized slabs which are thereby heated to or near graphitizing temperature before reaching the zone beneath the heat generating compartment where graphitization is completed. As a safe guard against slabs tending to jump over one another in traveling through the tunnel, a pair of holding down, or guide bars, 6l and 68, may

4 be placed over the slabs at each side of the top layer, as shown.

The following example is illustrative of the operation of a furnace constructed in accordance with the invention having a tunnel about 25 feet long and accommodating slabs 33.5 inches long` 9 inches wide, and 1.125 inches thick. Within the tunnel between the entrances, there are approximately 33 slabs in each layer laid side by side and moving in opposite directions periodically as additional slabs are shoved into the tunnel one each 4.5 minutes at each end. The heating compartment is about 40 inches long and 34.5

Y inches wide and has extending through it from side to side 4 resistors of graphite 8 inches wide and 1 inch thick. There is a space of about 1 inch between the resistors and the bottom closure 28 which is about 1.375 inches thick. The resistors carry about 14,000 to 15,000 amperes with a voltage drop of about 8.5 to 9.5 volts between the terminals. The consumption of electrical energy is as low as 0.25 kilowatt hour per pound of carbon concerted into graphite.

I claim:

1. In a graphitizing furnace, the combination of a shallow box-like compartment open at the sides and having rectangular top, bottom, and end walls, said compartment having its bottom horizontally disposed; resistance heating elements in the form of graphite slabs extending through the open sides of the compartment with one of the broad faces of the slabs parallel to and spaced from the said bottom; a horizontal tunnel below and contiguous to the said bottom, said tunnel extending beyond the ends of the compartment in opposite directions parallel to thel said bottom; a pair of rails extending lengthwise of the tunnel beneath the compartment, the transverse cross section of said tunnel being oblong with the long dimensions horizontally disposed and comprising means for the passage therethrough of slabs to be graphitized on being laid flat and across said rails in two layers, one upon the other, said tunnel having a horizontally disposed slot-like opening in each end thereof, the bottom of each said opening being on the same level as the top of the said rails; an upwardly sloping ramp outside one end of the tunnel, said ramp having its upper end adjoining the bottom of the adjacent tunnel opening; and another upwardly sloping ramp outside the other end of the tunnel, said another ramp having its lower end above the bottom of the adjacent tunnel opening.

2. In a graphitizing furnace, the combination of a shallow box-like compartment open at the sides and having rectangular top, bottom, and end walls, said compartment having its bottom horizontally disposed; resistance heating elements in the form of graphite slabs extending through the open sides of the compartment with one of the broad faces of the slabsY parallel to and spaced from the said bottom; a horizontal tunnel below and contiguous to the said bottom, said tunnel extending beyond the ends of the compartment in opposite directions parallel to the said bottom; a pair of rails extending lengthwise of the tunnel beneath the compartment, the transverse cross section of said tunnel being oblong with the long dimensions horizontally disposed and comprising means for the passage therethrough of slabs to be graphitized on being laid flat and across said rails in two layers, one upon the other; thermal insulation comprising lamp black disposed on and around the compartment and the portions of the tunnel extending beyond the compartment, said tunnel having a horizontally disposed slotlike opening in each end thereof, the bottom of each said opening being on the same level as the top of the said rails; an upwardly sloping ramp outside one end of the tunnel, said ramp having its upper end adjoining the bottom of the adjacent tunnel opening; and another upwardly sloping ramp outside the other end of the tunnel, said another ramp having its lower end above the bottom of the adjacent tunnel opening,

3. In a graphitizing furnace, the combination of a shallow box-like compartment open at the sides and having rectangular top, bottom, and end walls, said compartment having its bottom horizontally disposed; resistance heating elements in the form of graphite slabs extending through the open sides of the compartment with one of the broad faces of the slabs parallel to and spaced from the said bottom; a horizontal tunnel below and contiguous to the said bottom, 'said tunnel extending beyond the ends of the compartment in opposite directions parallel to the said bottom; a pair of rails extending lengthwise of the tunnel beneath the compartment, the transverse cross section of said tunnel beingl oblong with the long dimensions horizontally *disposed and comprising means for the passage. therethrough of slabs to be graphitized on being laid hat and across said rails in two layers, one upon the other; thermal insulation comprising lamp black disposed on and around the compartment CII and the portions of the tunnel extending beyond the compartment, said tunnel having a horizontally disposed slot-like opening in each end thereof, the bottom of each said opening being on the same level as the top of the said rails; an upwardly sloping ramp outside one end of the tunnel, said ramp having its upper end adjoining the bottom of the adjacent tunnel opening; another upwardly sloping ramp outside the other end of the tunnel, said another ramp having its lower end above the bottom of the adjacent tunnel opening; and reciprocating motor means including a piston rod at each end of the tunnel comprising means to shove slabs sidewise into the tunnel from each end and thence through the tunnel onto the ramp at the opposite end of the tunnel.

PAUL R. JUCKNIESS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 925,902 Harper et al. June 22, 1909 1,411,537 Sullivan Apr. 4, 1922 1,443,581 Little Jan. 30, 1923 2,279,511 Gottignies et al. Apr. 14, 1943 2,513,778 Bailey July 4, 1950 2,519,250 Jeppson et al Aug, 15, 1950 2,534,518 Jeppson Dec. 19, 1950 

